Define the Xdebug behaviour. Click Debug under the PHP node. On the Debug page that opens, specify the following settings in the Xdebug area:

In the Debug Port text box, appoint the port through which the tool will communicate with PhpStorm. This must be exactly the same port number as specified in the php.ini file:

xdebug.remote_port = <port_number>

By default, Xdebug listens on port 9000.

To have PhpStorm accept any incoming connections from Xdebug engines through the port specified in the Debug port text box, select the Can accept external connections checkbox.

Select the Force break at the first line when no path mapping is specified checkbox to have the debugger stop as soon as it reaches and opens a file that is not mapped to any file in the project on the Servers page. The debugger stops at the first line of this file and Debug Tool Window. Variables shows the following error message: Cannot find a local copy of the file on server <path to the file on the server> and a link Click to set up mappings. Click the link to open the Resolve Path Mappings Problem dialog box and map the problem file to its local copy.

When this checkbox cleared, the debugger does not stop upon reaching and opening an unmapped file, the file is just processed, and no error messages are displayed.

Select the Force break at the first line when the script is outside the project checkbox to have the debugger stop at the first line as soon as it reaches and opens a file outside the current project. With this checkbox cleared, the debugger continues upon opening a file outside the current project.

In the External Connections area, specify how you want PhpStorm to treat connections received from hosts and through ports that are not registered as deployment server configurations.

Ignore external connections through unregistered server configurations: Select this checkbox to have PhpStorm ignore connections received from hosts and through ports that are not registered as deployment server configurations. When this checkbox is selected, PhpStorm does not attempt to create a deployment server configuration automatically.

Break at first line in PHP scripts: Select this checkbox to have the debugger stop as soon as connection between it and PhpStorm is established (instead of running automatically until the first breakpoint is reached). Alternatively turn on the Run | Break at first line in PHP scripts option on the main menu.

Max. simultaneous connections: Use this spin box to limit the number of external connections that can be processed simultaneously.

Configuring Xdebug for using in the On-Demand mode

Starting with version 2016.2, PhpStorm supports the On-Demand mode where you can disable Xdebug for your global PHP installation, and have it enabled automatically on demand only when you are debugging your command-line scripts or when you need code coverage reports. This lets your command line scripts (including Composer and unit tests) run much faster.

Disable Xdebug for command-line scripts:

Open the Settings / Preferences Dialog by pressing Ctrl+Alt+S or by choosing File | Settings for Windows and Linux or PhpStorm | Preferences for macOS, and click PHP under Languages & Frameworks.

From the PHP executable drop-down list, choose the relevant PHP interpreter and click next to it. In the CLI Interpreters dialog box that opens, click the Open in Editor link next to the Configuration file: <path to php.ini> file. Close all the dialog boxes and switch to the tab where the php.ini file is opened.

In the php.ini file, find the [XDebug] section and comment the following line in it by adding ; in preposition:

;[XDebug]
;zend_extension = "<full_path_to_xdebug>"

Open the CLI Interpreters dialog box and click next to the PHP executable field. PhpStorm informs you that debugger is not installed:

To enable PhpStorm to activate Xdebug when it is necessary, specify the path to it in the Debugger extension text box, in the Additional area. Type the path manually or click and select the location in the dialog box that opens.

Configuring Xdebug for using in the Just-In-Time mode

PhpStorm supports the use of Xdebug in the Just-In-Time (JIT) mode so it is not attached to your code all the time but connects to PhpStorm only when an error occurs or an exception is thrown. The Xdebug operation mode is toggled through the xdebug.remote_mode setting, which is by default set to req. The mode is available both for debugging command-line scripts and for web server debugging.

Depending on whether you are going to debug command-line scripts or use a Web server, use one of the scenarios below.

Web server debugging

Choose Local Web Server or Shared Folder to check a debugger associated with a local Web server.

Path to Create Validation Script: In this field, specify the absolute path to the folder under the server document root where the validation script will be created. For Web servers of the type Inplace, the folder is under the project root.

The folder must be accessible through http.

URL to Validation Script: In this text box, type the URL address of the folder where the validation script will be created. If the project root is mapped to a folder accessible through http, you can specify the project root or any other folder under it.

Choose Remote Web Server to check a debugger associated with a remote server.

Path to Create Validation Script: In this field, specify the absolute path to the folder under the server document root where the validation script will be created. The folder must be accessible through http.